The invention relates to a one piece driveshaft produced by deformation and used especially in the drive line of a motor vehicle. The driveshaft is in the form of a tubular shaft with a central tube region with end pieces at each end which have toothed receiving regions to connect with torque transmitting elements.
DE-PS 30 09 277 illustrates a driveshaft for use as a side shaft in the drive line of a motor vehicle. The driveshaft substantially includes a tubular shaft comprising two ends with reduced diameters with joint receiving regions. The entire central region of the tubular shaft is cylindrical and is at a maximum outer diameter. In order to achieve a uniform mechanical strength across the entire region of the tubular shaft, the wall thickness is reduced with an increased outer diameter. The disadvantage of this design is that attention centers exclusively on the mechanical strength of the shaft. Only limited attention is paid to adjusting the natural frequency of the shaft to the respective requirements. Generally, the natural frequency is within the range of the excitation frequency of the engine/gearbox system so that avoidance of annoying vibration noise is impossible.
Furthermore, the art shows additional masses, which weigh between 0.5 and 2 kilograms, slid onto the central tube region of the driveshaft. The space for the driveshaft existing in motor vehicles is usually insufficient to optimally position these masses on the driveshaft. Also, the additional weight may have a negative effect on the bending and torsional frequencies as well. Such an increase in unsprung masses also adversely affects the driving behavior of the vehicle.
It is the object of the present invention to provide a driveshaft whose vibration behavior may be improved by using simple design measures to set the natural frequency to values within the frequency range of minimum external excitation, thereby reducing the vibration noise. In accordance with the invention, the objective is achieved by a central tube region having at least one axially limited additional mass element which is provided by a radially thickened shaft wall.
By forming the additional mass in the central tubular region of the driveshaft, it is possible to change the natural torsional frequency without adversely affecting the bending frequency. As a result, an optimized shaft is obtained which greatly improves the weight of the shaft, its load bearing capacity and NVH (noise, vibration, harshness) behavior. Such a driveshaft may be produced from a monoblock hollow shaft or a welded hollow shaft without causing any additional production and assembly costs. Also, the present invention maintains the symmetry of rotation of the driveshaft.
Alternatively, a plurality of additional mass elements may be partially distributed over the outer circumference of the driveshaft. The additional mass is formed by changing the inner and/or outer diameter in the central tube region. This provides an additional mass whose wall thickness may have any dimension relative to the wall thickness of the central region of the tubular shaft. The additional mass of the driveshaft may be arranged symmetrically or asymmetrically in the axial direction, thereby setting the natural frequency to values of minimum external excitation energy.
Experience has shown that by displacing the center of gravity towards one shaft end which, in the subsequent fitting condition in the vehicle, points towards the drive components with the greater mass, considerably reduces vibration noise.
For optimizing the natural torsional frequency, the additional mass, itself, should include a varying wall thickness. At least one additional mass may be arranged symmetrically or asymmetrically in the axial direction of the driveshaft so that, depending on the type of application, the symmetry of the driveshaft is maintained or the above-mentioned advantages are achieved, by giving the driveshaft an asymmetrical design by displacing the center of gravity in the axial direction. In the central tubular region of the driveshaft different masses may be combined for the purpose of optimizing the driveshaft.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.